In recent years, displays such as LCDs, PDPs, etc., have made progress, and products of various sizes which are used for a variety of purposes such as portable telephones, large screen TVs, etc., have been produced and sold. In general, a layer having an anti-reflection function is provided on the surface of these displays in order to further improve visibility. The anti-reflection technology includes an anti-glare film to prevent ambient light from being reflected and an anti-reflection coating for reducing the reflectivity thereof by using interference effects of light.
In conventional anti-glare techniques, as a method for roughening the surface of an anti-glare film, a method in which the surface of a substrate is directly roughened by a sandblasting method, an embossment method, etc.; a method in which a hard coat layer containing fillers is formed on the surface of a substrate; and a method in which a porous film is formed on the surface of a substrate by using a sea-island structure; etc., can be mainly used. Additionally, in a conventional anti-reflection technique, a method in which an anti-reflection film is formed by sputtering, etc., can be mainly used. However, a vacuum film forming method such as the latter sputtering, etc., is expensive and has insufficient adhesion with a plastic film, and it is difficult to form a film in which large areas are uniform, and therefore, recently a method in which multiple layers having different refractive indexes, respectively, are laminated by a wet coating, is used. Reflectivity of an antireflection film produced by the sputtering is usually 0.3% or less; however, reflectivity of a film produced by the wet coating is higher than that by the wet coating, and most may be about 1.0%, and this is called a low-reflection to distinguish it from the anti-reflection.
A low-reflection film produced by the wet coating has a standard structure in which a high refractive index layer and a low refractive index layer are laminated in this order on a substrate, and some optional layers may be added between the substrate and the high refractive index layer, between the high refractive index layer and the low refractive index layer, or on the low refractive index layer, as necessary. Here, the high refractive index and the low refractive index do not express absolute refractive indexes, and express higher or lower in refractive index in the case in which refractive indexes of two layers are relatively compared, and the reflectivity is lowest when both refractive indexes have the relationship in the following equation 1.n2=(n1)1/2  (equation 1)
(n1 is the refractive index of a high refractive index layer, and n2 is the refractive index of a low refractive index layer.)
In general, in material for a high refractive index layer of the low-reflection film produced by the wet coating, the refractive index is increased by using an organic polymer which contains the elements chlorine, bromine, sulfur, etc., or by dispersing ultrafine particles of metal oxide having high refractive index such as those of titania, zirconium oxide, zinc oxide, etc., in the layer. In addition, in the low refractive index layer, the refractive index is reduced by using fluorine containing organic polymers or silica, magnesium fluoride, etc., having low refractive index, or by forming holes using fine particles so as to mix.
In recent years, displays used in large screen TVs are in great demand, and as a result, low-reflection films produced by the wet coating are also in great demand. As a low-reflection film, a two-layer type structure in which a hard coat layer combining a function as a high refractive index layer, and a low refractive index layer are provided on a transparent film made of polyethylene terephthalate (PET), triacetylcellulose (TAC), etc., and a three-layer type structure in which a hard coat layer, a high refractive index layer, and a low refractive index layer are provided on the transparent film, are produced and have been sold. In the low-reflection film, high abrasion resistance, chemical resistance and contamination resistance, are required in addition to low reflectivity, and recently, antistatic property is also required on the surface thereof. The antistatic property is required by a demand of the market to prevent dust from adhering due to electrostatic charge, and moreover, improves wiping property of adhered dust, and surface electric resistance is required to be 107 to 1011 Ω/sq. The Ω/sq is a unit of surface resistance.
In order to give the antistatic property on the surface of an anti-glare film, it is necessary to give the antistatic property in any one layer or some layers of a hard coat layer, a high refractive index layer, and a low refractive index layer as well as the case of the above low-reflection film. As a material for giving the antistatic property, surfactants, electroconductive polymers, electroconductive inorganic fine particles, etc., are used, and in particular, a method in which electroconductive inorganic fine particles are dispersed into a coating film is mainly utilized, since it is effective for reducing electrical resistance.
It is preferable that the electroconductive inorganic fine particles be disposed nearest the surface from the viewpoint of the antistatic property; however, since these materials generally have a high refractive index, it is preferable that the materials be contained in a layer which is provided under the low refractive index layer and conductivity and high refractive index be given considering the anti-reflection.
As an example of the above anti-reflection, Japanese Unexamined Patent Application Publication No. 2003-294904 discloses anti-reflection structures having a two-layer type structure (electroconductive layer/low refractive index layer) or a three-layer type structure (electroconductive layer/high refractive index layer/low refractive index layer), and it is described that transparent conductive ultrafine particles of metal oxide are dispersed in the electroconductive layer, and that the particles include needle shaped or globular fine particles of antimony doped tin oxide and aluminum doped zinc oxide. In addition, Japanese Unexamined Patent Application Publication No. 2002-167576 discloses an electroconductive material composition having high refractive index which includes electroconductive fine particles (A component), dielectric fine particles (B component) having a refractive index of 2.0 or more, and binder (C component), and in which the contents of the B component and C component are 5 to 100 weight parts to 100 weight parts of the A component, respectively. It is described that the electroconductive fine particle is chosen from indium tin oxide, tin oxide, antimony tin oxide, and zinc aluminum oxide. Furthermore, Japanese Unexamined Patent Application Publication No. 2001-302945 discloses a UV curable transparent conductive coating material composition that includes tetragonal tin oxide fine particles produced by a plasma method, acrylate compound, and alcohols.
Other patent applications disclose antistatic and high refractive index of anti-glare films; however, an anti-glare film in which low reflectivity, antistatic properties, abrasion resistance, chemical resistance, contamination resistance, etc., are balanced, has still not been realized.
In addition, as a method for giving simultaneously these functions such as low reflectivity, antistatic, abrasion resistance, chemical resistance, and contamination resistance, films in which layers are laminated have been developed; however, formation of multiple layers requires a process for coating on a substrate any number of times and production cost is increased. Furthermore, it is difficult to adjust the balance between each layer by the formation of multiple layers, and in practice, some of these functions is merely chosen depending on the intended use.